The present invention relates to a printing apparatus and a printing method, in which an image is formed by that a print head having a plurality of printing elements scans a printing medium in two orthogonal directions, that is, a main scanning direction and a sub scanning direction, in particular, which can achieve high quality of a printed image and can reduce maximum current consumed in its driving circuit.
In order to achieve the high quality of the printed image, the disposition of printing elements must be in high density to meet high printing resolution. However, it is not easy to dispose the printing elements in high density at the manufacturing, therefore, a print head in which the pitch of printing elements is wider than the pitch of printing pixels is used. In case that the print head in which the pitch of printing elements is wider than the pitch of printing pixels is used, pixels printed by one time scanning have a space of a slit type among them.
Conventionally, in order to fill in the space, a series of sub scanning operation corresponding to the pitch of printing pixels is repeated after the printing was performed in the main scanning direction, and the print of a band area whose width is the length of the printing element array is completed. And, an image is segmented into bands beforehand and the printing operation mentioned above is repeated for the number of band areas, and the printing for whole image is performed. However, at this print operation, the sub scanning operation of the length of the printing element array is required.
However, at this sub scanning operation of the length of the printing element array, errors are liable to occur caused by the large amount of scanning, and this causes to form a blank space or an overlapped space among band areas. This blank or overlapped space appears as a white streak or a black streak extending in the main scanning direction and causes the deterioration of the printed image. This white or black streak extending in the main scanning direction is named as banding.
This banding is a common phenomenon at a printing apparatus in which a print head having a plurality of printing elements forms an image by scanning for a printing medium in two orthogonal directions, that is, in the main and sub scanning directions. An interlaced print scheme is a technology to solve this banding problem. U.S. Pat. No. 4,198,642 discloses an ink jet printer having an interlaced print scheme and describes conditions for the interlaced print scheme in which the amount of the sub scanning is a constant.
According to this U.S. Pat. No. 4,198,642, when the number of printing elements has no prime factors greater than one in common with the result that the pitch of printing elements is divided by the pitch of printing pixels, the interlaced print scheme, in which the amount of the sub scanning is a constant, can be performed, by making the amount of the sub scanning the product of the pitch of printing pixels times the number of the printing elements. At this time, the amount of the sub scanning is lower enough than the length of the printing element array, therefore, forming of the banding can be prevented.
And U.S. Pat. No. 4,069,486 and Japanese Patent Application Laid-Open No. SHO 53-2040 disclose a single array ink jet printer in which a main scanning is performed by using a dram mechanism, and describe conditions in case that a plurality of printing elements are used, similarly as the U.S. Pat. No. 4,198,642 mentioned above.
Further, as another technology to prevent the banding, there is a process named a shingling process. At this shingling process, a part of a print by one time main scanning is excluded and interpolation is performed by making printing elements pass through plural times each one line in the main scanning direction of an image. Japanese Patent Application Laid-Open No. HEI 3-207665 discloses a printing method, in which a shingling process is described. In this shingling process, a print head having a plurality of printing elements disposed in the sub scanning direction with the same interval of the pitch of printing pixels is used, and the print is performed by excluding xc2xd in the main scanning direction.
Each in Japanese Patent Application Laid-Open No. HEI 10-67126 and Japanese Patent Application Laid-Open No. HEI 10-157137, a technology to exclude the banding effectively is disclosed, by combining an interlaced print scheme under the condition in which the amount of the sub scanning is a constant with the shingling process.
However, requiring image quality has become high in response to the technical improvement such as in the print head, and excluding the banding effectively has not been achieved sufficiently by the methods mentioned above. Especially, it is difficult to achieve requiring image quality by only applying either the interlaced print scheme or the shingling process, and it is necessary to utilize both the interlaced print scheme and the shingling process.
On the other hand, maximum current requiring instantaneously increases corresponding to the increase of the number of nozzles provided in the print head, and this maximum current requiring instantaneously must be reduced. When by making large current flow in order to drive many printing elements, a voltage waveform of power amplifier driving the printing elements is changed, and the image quality is deteriorated. In order to avoid changing the voltage waveform, it is possible to use a power amplifier having larger capacity, but it causes the cost of the power amplifier to increase. At the Japanese Patent Application Laid-Open No. HEI 10-67126 and Japanese Patent Application Laid-Open No. HEI 10-157137 that use both technologies, the interlaced print scheme and the shingling process, it is not described to reduce the maximum current.
It is therefore an object of the present invention to provide a printing apparatus and a printing method, in which an image is formed by scanning a print medium in two orthogonal directions, that is, in a main scanning direction and a sub scanning direction, with a print head having a plurality of printing elements, and which utilize both an interlaced print scheme and a shingling process, and make maximum current low by utilizing the excluding operation of a part of printing by the shingling process, and can achieve to prevent banding in high efficiency and also to realize the low cost.
According to the present invention, the printing apparatus provides a print head having a plurality of printing elements that are disposed in the sub scanning direction, a first means which selects printing elements to be used for printing from the plurality of printing elements and divides the selected printing elements into P (P is an integer two or more) pieces of printing element groups in which the number of printing elements m in each of the P pieces of printing element groups is equal, a second means which allocates one of the P pieces of printing element groups to one of printing pixels to be printed, and a third means which sets a scanning amount in the sub scanning direction so that one of the printing elements in each of the P pieces of different printing element groups passes through one of the printing pixels for all printing pixels on the printing medium.
Therefore, the printing apparatus of the present invention can utilize both the interlaced print scheme and the shingling process, and make maximum current low by utilizing the excluding operation of a part of printing by the shingling process, and can achieve to prevent the banding in high efficiency and also to realize the low cost.
According to the present invention, the printing method, in which an image is formed on a printing medium by that a print head having a plurality of printing elements moves in two orthogonal directions, that is, a main scanning direction and a sub scanning direction, provides the steps of, selecting printing elements to be used for printing from the plurality of printing elements, dividing the selected printing elements into P (P is an integer two or more) pieces of printing element groups in which the number of printing elements m in each of the P pieces of printing element groups is equal, allocating one of the P pieces of printing element groups to one of printing pixels to be printed, and setting a scanning amount in the sub scanning direction so that one of the printing elements in each of the P pieces of different printing element groups passes through one of the printing pixels for all printing pixels on the printing medium.
With the method mentioned above, the print head is supposedly regarded as a head in which independent P pieces of heads whose printing elements are the same are unified. And the main scanning and the sub scanning are controlled so that each of the P pieces of printing element groups can print all of the printing medium by itself, and each of the P pieces of printing element groups which print every printing pixel is selected so that the printing pixels are not printed in overlap. With this, the shingling process can be realized. In this, when the printing elements are grouped, the number of the printing elements in each of the P pieces of printing elements groups must be the same, therefore, the number of the printing elements to be used is adjusted and there is a case that some of the printing elements are not used. And the interlaced print scheme can be performed in case that the pitch of the printing elements is wider than the pitch of the printing pixels, and even in case that the amount of the sub scanning is not a constant. Therefore, the interlaced print scheme and the shingling process can be performed at the same time. And the printing elements are divided into groups and one of the printing element groups is selected and driven, as a result, all of the printing element group are not driven at the same time. Consequently, the maximum current to the print head is made to be low and the cost of the circuit can be reduced.